Stroke is one of the most devastating medical conditions our society faces. The American Heart Association reports that stroke occurs every 45 seconds, accounting for 1 in 16 deaths, with about 750,000 cases in the United States in 2008. It is the second leading cause of death worldwide and the number one reason for nursing home admissions each year in the United States. It can affect individuals at any age, including the very young.
Stroke occurs when the arteries leading to, or within, the brain become interrupted. Such a blood vessel may become blocked (ischemic stroke) or may rupture (hemorrhagic stroke). Ischemic stroke, caused by blockage of blood flow, is the most common type of stroke. Once the brain is deprived of blood, and thereby the oxygen which it carries, affected brain tissue becomes dysfunctional and ever increasing, potentially irreversible, tissue damage ensues.
Stroke represents a medical emergency and is a potentially reversible process. When large vessels are involved, stroke may be associated with the irreversible destruction of approximately one hundred and twenty million neurons each hour the obstructing lesion (“thrombus”) goes untreated. Rapid reperfusion and removal of the thrombus is critically important. The obstructing lesion that interrupts the carotid arterial or cerebral arterial circulation may originate from below the brain, such as in the heart, or form in situ within the arterial circulation itself. Large vessel strokes most frequently involve the territory of the Middle Cerebral artery. Shortly after a thrombus interrupts blood flow to a large artery in the brain, the “Core” area of brain tissue, most severely lacking in blood flow, will begin a process of irreversible cell damage. This area is surrounded by a zone (“the Ischemic Penumbra”) that eventually will be irreversibly damaged if blood is not restored within short order. The goal of stroke therapy is to provide blood flow to the “Core” and “Penumbral” areas as rapidly as possible. While there are many types of stroke symptoms, indicative of ischemia to these regions, the most common symptoms are sudden numbness or weakness in the face, arm, and/or leg on one side of the body. Rapid symptom recognition and transport to an appropriate hospital is critical so that treatment to reverse this ischemic process can be attempted.
Prior to 1996, no approved treatment to reverse brain ischemia in acute stroke was available. In 1996 the pharmaceutical compound tissue plasminogen activator (t-PA) received approval by the Food & Drug Administration (FDA) for the treatment of acute ischemic stroke. This drug could, in some cases, stop and reverse stroke by dissolving the obstructing thrombus. The benefit of t-PA, however, is limited in that it has significant clinical benefit in only approximately 12% of patients who receive it as therapy for acute ischemic stroke. Furthermore, in the case of ischemic stroke due to obstruction at the level of the large proximal vessels of the brain, i.e., proximal Middle Cerebral Artery, Basilar, or Internal Carotid Artery less than 10% of patients treated benefit significantly. Current FDA restrictions limit utilization of t-PA to administration within three hours from onset of stroke symptom. Furthermore, numerous other exclusion criteria exist such that less than 5% of patients who experience a stroke in the United States actually receive t-PA yearly. Due to an ever increasing number of people over age 65 (and the expected 2.5-fold increase in atrial fibrillation over the next 50 years) a steady rise in the number of strokes due to large vessel embolic occlusions is expected. As the population ages, therefore, not only is the total number of ischemic stroke per year expected to increase but so is the percentage of strokes amenable to endovascular therapies. This underscores the tremendous opportunity to develop a rapid neuro-protectant device whose function is immediate large vessel arterial reperfusion. As the total cost to society of ischemic stroke for the period of 2005 to 2050 was recently projected to be $2.2 trillion the introduction of new technologies to mitigate stroke impact are of the utmost priority.
New devices designed for mechanical thrombectomy in acute ischemic stroke have been approved for use by FDA. One such device, the “MERCI” device (“Mechanical Embolus Removal in Cerebral Ischemia”, manufactured by Concentric Medical, Mountain View, Calif.) is used to extracting and removing thrombus from the brain of acute stroke patients. A second endovascular device, operating on the principle of suction (the Penumbra device), has also received FDA approval for use in patients with acute ischemic stroke.
Although FDA approval oft-PA and certain endovascular devices represents a significant advancement in the field of stroke medicine, the majority of patients experiencing large strokes today still demonstrate poor outcomes. Therefore, there still exists a great need for improved devices and methods for rapid cerebral tissue reperfusion for patients experiencing acute ischemic stroke. The present invention, addresses this and many other needs in this area.